1. Field of the Invention
This invention relates to an electrowetting system. More specifically, it relates to an electrowetting system for the smooth continuous movement of a droplet across a single circuit using a continuous applied direct current voltage.
2. Description of the Prior Art
Recent technical advances have enabled the manipulation of small volumes of fluids—often in discrete droplets. Many of these systems utilize the phenomena of electrowetting to manipulate the small electrical droplets. Electrowetting on dielectric (EWOD) is the reduction in apparent contact angle of a fluid droplet using the capacitance of a dielectric layer which lies between the droplet and an electrode. Applying voltage across this barrier (between the droplet and electrode) causes charge migration to occur within the droplet and electrode, which modifies the apparent surface energy of the droplet, causing its apparent contact angle to be reduced.
Applications for electrowetting, in general, are diverse, ranging from the shaping of microlenses, fiber optics switching, display technology, and optical filters, to such interesting areas as the creation of small low-power-consumption motors. When looking at applications for EWOD droplet transport, the most significant (with much interest and diversity of research) is lab-on-a-chip designs. Also, the use of droplet motion to assist in assembly of nano- and micro-scale components for microdevices holds promise.
Droplet movement by asymmetric electrowetting (where only a portion of the droplet has its contact angle reduced causing droplet motion) is known in the prior art. The prior art uses successive activation of discrete small electrodes, several of which are covered by the droplet. As each electrode is activated and the contact angle above it reduced, the droplet is “handed off” from electrode to electrode. This accomplishes droplet movement in successive discrete steps each having a magnitude equivalent to the size of the electrodes and requires complex control systems to control the activation of electrodes in the proper sequence and with the proper timing. Moreover, because electrowetting behavior is related to the voltage squared, it is typically shows no significant dependence on voltage polarity.
Accordingly, what is needed is an electrowetting system for the smooth continuous movement of a droplet across a single circuit using a continuous voltage.
What is also needed is an electrowetting system that is dependent on the polarity of the applied voltage, i.e., the actuation direction changes with a change in voltage polarity.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the art how the limitations of the art could be overcome.